The invention relates to a thermal ink jet composition, a printing process and a method of improving the fast dry characteristics of inks.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or to a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Quality thermal ink jet printing can be achieved by utilizing an aqueous ink composition containing at least one dye or pigment, a wetting agent and water. U.S. Pat. No. 4,508,570 to Fujii et al., discloses an aqueous ink for ink jet printing, which comprises a water-soluble direct dye and/or acid dye, a polyhydric alcohol and/or an alkyl ether thereof, water, and at least one water-soluble non-ionic surface active agent selected from a specified polyoxyethylene alkyl amine, a specified polyoxyethylene alkyl phenyl ether and a specified polyoxyethylene alkyl ether. U.S. Pat. No. 4,623,689 to Shintan/et al., discloses an ink jet ink containing aqueous colored polymers, which comprise a homopolymer of an ethylenically unsaturated sulfonic acid or its salt or a copolymer of an ethylenically unsaturated sulfonic acid or its salt with another ethylenically unsaturated monomer, wherein the homopolymer or copolymer is dyed with a basic dye and has a lowest film-forming temperature of not higher than 35.degree. C. U.S. Pat. No. 4,627,876 to Fries et al., discloses a printing ink containing a pigment and an alkyd resin binder. The resin binder is modified with fatty acids. The alkyd resin is the reaction product of (a) a fatty acid, triglyceride of a fatty acid or a mixture of fatty acids, (b) a polyol, (c) an epoxy resin and (d) a dicarboxylic acid.
U.S. Pat. No. 4,026,713 to Sambucetti et al. relates to a magnetic ink containing non-ionic, cationic and/or anionic surfactants. The surfactants may include glycerol, a lower alkyl monoether of ethylene glycol and/or a polyethylene diol.
U.S. Pat. No. 4,914,562 to Abe et al. discloses an ink jet composition containing an ionic surface active agent or a non-ionic surface active agent. The ionic surface active agent can be a dioctyl sulfosuccinate sodium salt, sodium oleate or dodecylbenzenesulfonic acid. The non-ionic surface active agent may be diethylene glycol mono-n-butyl ether or triethylene glycol mono-nbutyl ether.
U.S. Pat. No. 5,019,166 to Schwarz relates to a thermal ink jet printing composition comprising a dye, a liquid medium and a surfactant selected from the group consisting of polyoxyalkylated ethers, anionic bitail fluorothio alkyls, alkyl aryl sulfonates, alkyl amine quaternary salts and mixtures thereof.
U.S. Pat. No. 5,116,409 to Moffatt discloses a process for reducing color bleed of inks employed in thermal ink jet printing. The process comprises printing two inks side by side, each ink having a composition comprising (a) a vehicle and (b) about 0.1 to 10 wt. % of at least one water-soluble anionic dye. The vehicle comprises at least one member selected from the group consisting of zwitterionic surfactants and non-ionic amphiphiles and water or water and an organic solvent. Moffatt discloses a composition that includes SURFYNOL 5465, an acetylenic polyethylene oxide, and 1,5pentanediol.
U.S. Pat. No. 5,254,159 to Gundlach et al. discloses an ink composition that comprises water, an anionic dye and an amine compound. The ink composition provides waterfast images. The disclosure of this patent is incorporated in its entirety herein by reference.
Full color printing in a thermal ink jet printing process requires an ink with fast dry characteristics. Fast dry characteristics can be improved by the addition of a penetrant. The penetrant can be a quasisurfactant penetrant. For the purposes of this invention, the quasisurfactant penetrant has a hydrophilic head and a tail that is hydrophobic but too short to impart the properties of a strong surfactant like sodium lauryl sulfate. While surfactants with long hydrophobic tails typically form micelles at very low concentrations, the quasisurfactant penetrants do not form micelles. A preferred quasisurfactant penetrant is a surfactant that is substituted with a polar substituent toward one end of a chain of 4-8 aliphatic carbon atoms. Exemplary penetrants include dl-1,2-hexanediol, 1,2-octanediol, diethylene glyco butyl ether (or 2-(2-butoxethoxy)ethanol, 1-cyclohexyl-2-pyrrolidinone, 2-methyl2-propyl-1,3-propanediol and 1-butanesulfonic acid sodium salt.
A penetrant imparts quick-dry characteristics to a thermal ink jet ink composition. However, effectiveness of a penetrant in providing quick-dry characteristics varies with ink composition solvent. Some penetrants do not provide acceptable quick-dry characteristics to some ink-solvent systems. Cosolvents can be added to ink compositions to improve effectiveness of the surfactant penetrant or penetrant concentration in the ink compositions can be increased to achieve satisfactory quick-dry characteristics. However, some cosolvent packages and/or higher penetrant concentrations cause deterioration of thermal ink jet hardware. For example, higher loads of diethylene glyco butyl ether or higher loads of cyclohexyl pyrrolidinone aggressively attack cartridge materials and seals.
The incorporation of salts into inks containing organic non-ionic penetrants can aid in phase separation of an organic cosolvent through a "salting out" effect. Phase separation can reduce dry time of an ink on paper. This effect is observed for the incorporation of ionic salts such as sodium chloride. However, ionic salts destabilize ink compositions causing dye to precipitate.
The present invention relates to an improved thermal ink jet printing composition with reduced dry time. The composition is characterized by improved stability.